6mm lathe drawbar thread advice

skinnb1

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Oct 4, 2015
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I have a reasonably equipped 6mm lathe which I use from time to time as an enthusiastic amateur. I haven't found a manufacturer's mark. Someone has written Wolf Jahn on the box and Lorch collets and a Lorch 3-jaw chuck fit the drawbar without any problem.

I have recently acquired a faceplate but the thread on the faceplate and the thread on my drawbar appear to be incompatible. The threads seem undamaged but only the first thread engages and then jams.

I am puzzled as the De Carle book which lists the dimensions from Crawford's table of collet dimensions shows all 6mm collets as having the same dimensions and threads. The external diameter of the threaded portion of the collet on the faceplate is .199 inches.

I suppose I could attempt to make a drawbar with a matching thread or attempt to alter the thread on the faceplate but threads are a bit of a mystery to me.

Any advice on the best way to proceed please?
 

gmorse

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Hi skinnb1,

What happens when you closely compare the thread on your faceplate with one on a correctly fitting collet? Do they have different pitches and/or diameters? Does the faceplate collet seat fully in the headstock cone without the drawbar?

Regards,

Graham
 

measuretwice

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There's more theads than in De Carles book. Don't let threads be a mystery, they're a just a helix with three things defining them: diameter, pitch (spacing of the threads) and the thread profile (60 degrees, acme, buttress etc). The usually approach is to measure diameter and pitch then find a matching standard thread. Of course with old specialist stuff threads often predate standards or are custom to suit the function of the part.

I'd start by measuring the pitch and confirming with a loupe that its a V profile thread (probably is, but there are a few buttress threads in horology). Identifying what it will fit, selling it as such and getting another would be the practical solution. I'd only consider modification if you isolated exactly what the discrepancy was - i.e. same thread but the faceplate's diameter was a a thou or two too large. Holding the collet and faceplate threads together should tell you if the pitch this the same. Making a drawbar in all likelihood means single pointing a rather small female thread or making a tap...both are doable but that requires a screw cutting lathe and knowledge of threading
 

skinnb1

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Hi skinnb1,

What happens when you closely compare the thread on your faceplate with one on a correctly fitting collet? Do they have different pitches and/or diameters? Does the faceplate collet seat fully in the headstock cone without the drawbar?

Regards,

Graham
Thanks for your interest Graham. I have very much enjoyed your Zoom talks recently.
I find it hard to answer authoritatively. I have photographed the threads of a 'good' collet marked Lorch and the faceplate collet side by side, the 'good' collet on the drawbar, the faceplate on the drawbar as far as it will go and the faceplate inserted in the headstock without the drawbar.
The first picture seems to suggest that the diameters of the two collets differ but they both measure .198 inches across the threads on my callipers.

I assume the threads are different but I lack the skill and understanding to measure them properly.

Brian

20210228_160600a.jpg 20210228_160647a.jpg 20210228_160724a.jpg 20210228_160824a.jpg
 

measuretwice

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that thread on the faceplate is looks quite damaged....did you compare pitches? Fix might be as simple as setting the faceplate in a screw cutting lathe and carefully chasing it
 

Jerry Kieffer

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I have a reasonably equipped 6mm lathe which I use from time to time as an enthusiastic amateur. I haven't found a manufacturer's mark. Someone has written Wolf Jahn on the box and Lorch collets and a Lorch 3-jaw chuck fit the drawbar without any problem.

I have recently acquired a faceplate but the thread on the faceplate and the thread on my drawbar appear to be incompatible. The threads seem undamaged but only the first thread engages and then jams.

I am puzzled as the De Carle book which lists the dimensions from Crawford's table of collet dimensions shows all 6mm collets as having the same dimensions and threads. The external diameter of the threaded portion of the collet on the faceplate is .199 inches.

I suppose I could attempt to make a drawbar with a matching thread or attempt to alter the thread on the faceplate but threads are a bit of a mystery to me.

Any advice on the best way to proceed please?
Lets assume the thread pitch and diameter are the same as your collets that thread in the drawbar as others have commented on, and you are not equipped to deal with this.

I would suggest as follows.

(1) Close inspection of the first and third photos in post #4 would indicate that the faceplate thread is damaged as measuretwice has mentioned.

(2) At this point I would mount the face plate in a Lathe per first attached photo setup to rotate slowly in reverse rotation.

(3) I would then purchase (If you do not have them) a fine micro knife or feather file per second and third photos.

(4) With the face plate spinning in reverse, engage the sharp edge of the file in the bottom end. (fourth photo , file is oversized for handy illustration) It will now follow the thread out to the end. Repeat as many times as it takes to fit the thread.

Jerry Kieffer

fullsizeoutput_7fe.jpeg fullsizeoutput_800.jpeg fullsizeoutput_7ff.jpeg DSCN1251.JPG
 

Jerry Kieffer

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Forgot to suggest a method of obtaining a thread pitch.

Measure across a number of threads with a gage pin or whatever that will span between thread point to point per attached photo under optics.

From this point you can divide the number of threads by the diameter of the measuring devise. From point to point will give you the thread pitch distance thus the thread pitch calculation when divided into a inch or mm.

Jerry Kieffer



DSCN5064.JPG
 

wefalck

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As others said the thread appears to be rather damaged, meaning that the tips of the threads have been pushed down. In this case the diameter over the tips as per Jerry's last image should be less than that of a 'good' collet, or what de Carlé wrote in his book.

If this is so, one can try to re-cut the threads. Using a thread-repair file is one option, but can be quite tedious, given that the whole thread appears to be damaged. Another option is to obtain a suitable die. Luckily such dies are again available on the market. Just search ebay et al. There is a German seller on ebay, who is very reliable, but I think he gets his stuff from Chinese sources. If you are based in the USA, you might be better off to buy directly in China. I am not aware of 6 mm dies from manufacturers in the USA, I have only seen 8 mm dies.

If the outside diameter is not smaller than the nominal diameter of a healthy 6 mm thread, you may have perhaps got a piece of 6.5 mm equipment. Boley and Wolf, Jahn & Co. made 6.5 mm lathes (not sure why ...). Check the pitch of the thread - take a length of say 1/2" on your vernier caliper and count how many tips there are over that length. If the pitch is correct for your draw-bar, you can use the above mentioned die and re-cut the thread for your 6 mm lathe.

I think a die is preferable in this case over trying to re-cut the thread on another lathe with a single point tool, because there centering will be quite difficult.

Having a die for the collet thread is always useful, because you can chase damaged threads or make your own spindle tooling ...
 

Jerry Kieffer

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As others said the thread appears to be rather damaged, meaning that the tips of the threads have been pushed down. In this case the diameter over the tips as per Jerry's last image should be less than that of a 'good' collet, or what de Carlé wrote in his book.

If this is so, one can try to re-cut the threads. Using a thread-repair file is one option, but can be quite tedious, given that the whole thread appears to be damaged. Another option is to obtain a suitable die. Luckily such dies are again available on the market. Just search ebay et al. There is a German seller on ebay, who is very reliable, but I think he gets his stuff from Chinese sources. If you are based in the USA, you might be better off to buy directly in China. I am not aware of 6 mm dies from manufacturers in the USA, I have only seen 8 mm dies.

If the outside diameter is not smaller than the nominal diameter of a healthy 6 mm thread, you may have perhaps got a piece of 6.5 mm equipment. Boley and Wolf, Jahn & Co. made 6.5 mm lathes (not sure why ...). Check the pitch of the thread - take a length of say 1/2" on your vernier caliper and count how many tips there are over that length. If the pitch is correct for your draw-bar, you can use the above mentioned die and re-cut the thread for your 6 mm lathe.

I think a die is preferable in this case over trying to re-cut the thread on another lathe with a single point tool, because there centering will be quite difficult.

Having a die for the collet thread is always useful, because you can chase damaged threads or make your own spindle tooling ...

Wefalck
I would normally agree and suggest the purchase of a 6mm tap and die if owning a 6mm Lathe and collets.

Unfortunately, they appear to be only available from China other than custom made from shops that specialize in taps and dies

Personally, I can not justify recommending Chinese tooling to anyone without them knowing what they have in their hand and the knowledge/experience to evaluate what is happening during use. An excellent example is as follows with three dies.

The first photo shows three special pitch dies, left side from China, middle from Poland and the third one on the right I machined.

The second photo, shows a close up of the threads on the die from China. In this case the threads are so rough that they mainly " scrape" the metal rather than cut. Its not something I would risk on anything of value.

The third photo thread is from the Die from Poland. (Middle first photo) These and others have been serviceable at a fair price but not all special thread pitches required have been available, thus the need to machine some of my own.

The fourth photo shows the thread of the third Die on the right in the first photo. The thread was single point cut on the Lathe.

Just another point of view.

Jerry Kieffer


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wefalck

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With due respect, Jerry, to your knowledge, workmanship and achievements, I don't think such comparison is fair or constructive, because:

1. you cannot compare a supermarket die with a purpose made one
2. every country in the world has good and bad products
3. I believe, if you pay the right Chinese company 150€ for a die, they can mass produce them at Levin or Schaublin qualitiy

Someone, who has the capabiity to make such a die in his own workshop, almost certainly could set up the face-plate for single-point re-threading. But this is not the point here. The point is to find for skinnb1 a solution for making his face-plate work with limited workshop capabilities and at least cost possible.

A common mistake people make is to recommend the 'best' tool, while they should be recommending the 'right' tool. Here the objective is to chase the thread, so that it can be held securely in the draw-tube, not to produce a factory-ground thread appearance.

Some 20 years ago, in the early Internet days, I bought a couple of 8 mm dies and taps from an USA source, because at that time they were the only ones available (I think I paid some 80 US$ for each set). Now you can get them also from traders say in the UK or in Germany, who have them made in China, I believe. The Chinese also sell them directly on the Internet. I am aware of only one current offer on ebay for 6 mm dies and taps, but I think in the past I got a tap and a die from a well-known trader in the UK. I am not aware of any source for 6 mm taps and dies in the USA, but I don't watch this market very closely anymore since the US Postal Service has discontinued 'surface mail', making shipping from the USA probibitively expensive.
 

skinnb1

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Thanks all for applying your experience and skill to this. With limited resources I have now managed to get photos of the threads under magnification. The calliper jaws are set to .2 inches. Under magnification the faceplate thread certainly looks worn. I believe the thread counts are the same.

It's great to have your collective experience applied to a stumbling beginner with a background in software engineering and bruised knuckles from car restoration but limited experience with clocks and watches. Acquiring new knowledge and skills is stimulating especially under Covid lockdown. I'll consider how to go from here.

The first photo shows the thread of Lorch collet which fits and the second shows the faceplate thread

210301114507388955515.jpg

210301114146388754843.jpg
 

gmorse

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Hi skinnb1,

The threads on the faceplate are clearly flattened and spread at the tips.

Setting the suspect thread against a known good one like this would negate the need for measurement.

DSC00796.JPG

If you paid money for it, I should request a refund!

Regards,

Graham
 
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Jerry Kieffer

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With due respect, Jerry, to your knowledge, workmanship and achievements, I don't think such comparison is fair or constructive, because:

1. you cannot compare a supermarket die with a purpose made one
2. every country in the world has good and bad products
3. I believe, if you pay the right Chinese company 150€ for a die, they can mass produce them at Levin or Schaublin qualitiy

Someone, who has the capabiity to make such a die in his own workshop, almost certainly could set up the face-plate for single-point re-threading. But this is not the point here. The point is to find for skinnb1 a solution for making his face-plate work with limited workshop capabilities and at least cost possible.

A common mistake people make is to recommend the 'best' tool, while they should be recommending the 'right' tool. Here the objective is to chase the thread, so that it can be held securely in the draw-tube, not to produce a factory-ground thread appearance.

Some 20 years ago, in the early Internet days, I bought a couple of 8 mm dies and taps from an USA source, because at that time they were the only ones available (I think I paid some 80 US$ for each set). Now you can get them also from traders say in the UK or in Germany, who have them made in China, I believe. The Chinese also sell them directly on the Internet. I am aware of only one current offer on ebay for 6 mm dies and taps, but I think in the past I got a tap and a die from a well-known trader in the UK. I am not aware of any source for 6 mm taps and dies in the USA, but I don't watch this market very closely anymore since the US Postal Service has discontinued 'surface mail', making shipping from the USA probibitively expensive.
Wefaick
In post # 6, I offered a practical inexpensive option based on how the OP indicated he or she is equipped. In this case the setup shown can be duplicated on the lathe it is to be mounted on. The use of the file as indicated, has produced excellent results where a die has not been available on one off items.

In post #9, I simply shared my personal experience with readily available products from various sources. It is true that you can hire anyone to do anything for the right price, but the average person has little choice but to deal with what is readily available where price is a consideration.
I my experience, equal quality has cost about the same regardless of its source.

The machined die simply points out another inexpensive option (about 50 cents) for those who are equipped to do so, but may not have considered it.
While I can see your point, It was not intended as any type of achievement since its a common metal working practice.

Jerry Kieffer
 
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